1. Field of the Invention
The present invention relates to a process for surface-mounting a semiconductor chip onto a circuit board in a reliable manner.
2. Description of the Related Art
As a process, as described above, there has been known a mounting process illustrated in FIGS. 5 and 6. In FIG. 5, a resinous ACF 30 having a larger width than a semiconductor chip 20 is prepared, and then the semiconductor chip 20 is mounted onto a surface of a circuit board 10 via the ACF 30 whilst the ACF 30 extends beyond of the periphery of the semiconductor chip 20.
Next, as shown in FIG. 6, the ACF 30 and the peripheral region are heated while pressing the semiconductor chip 20 onto the circuit board 10. Thereby, thermosetting resin of the ACF 30 may be heated to approximately 180.degree. C. for approximately several tens of seconds to be cured, or thermoplastic resin of the ACF 30 may be cooled and hardened after the heating. Thus, the semiconductor chip 20 is bonded via the resin of the ACF 30 onto a surface of the circuit board 10.
Electroconductive particles contained in the resin of the ACF 30 are interposed between conductive bumps 22 formed on electrodes of the semiconductor chip 20 and terminals 12 formed on the surface of the circuit board 10, so that the electric connection is obtained between the conductive bumps 22 of the semiconductor chip 20 and the terminals 12 of the circuit board 10 via the electroconductive particles.
In this regard, "ACF" is an abridgement of "anisotropic conductive film" made, for example, of thermosetting resin such as epoxy resin or of thermoplastic resin such as polyethylene. The ACF has electroconductive particles in the resin forming the same. When the semiconductor chip is surface-mounted on the circuit board as described above, it is possible to interpose the electroconductive particles contained in the ACF resin between the conductive bumps formed on the electrodes of the semiconductor chip and the terminals formed on the surface of the circuit board. Also, it is possible for an area of the ACF interposed between the conductive bump of the semiconductor chip and the terminal of the circuit board to be electrically conductive. Thus the electric connection is obtainable between the conductive bump of the semiconductor chip and the terminal of the circuit board via the electroconductive particles contained in that portion of the ACF resin.
According to this mounting process, the semiconductor chip 20 is bonded onto the surface of the circuit board 10 via the resin of the ACF 30. Together therewith, it is possible to electrically connect the conductive bump 22 formed on the electrode of the semiconductor chip 20 with the terminal 12 on the surface of the circuit board 10. Thus, the semiconductor chip 20 can be surface-mounted, without being stripped off, on the circuit board 10 in a reliable manner.
When the semiconductor chip 20 is surface-mounted onto the circuit board 10 in a manner as described above, however, it is impossible to assuredly adhere the resin of the ACF 30 extended out of the periphery of the semiconductor chip 20 to the upright lateral surface 24 thereof while raising the resin upward.
Therefore, when the semiconductor chip 20 has been surface-mounted onto the circuit board 10 by the above-mentioned process, the resin of the ACF 30 is liable to be stripped off in use from the peripheral portion of the semiconductor chip 20, whereby it is impossible to continue the favorable connection of the conductive bump 22 formed on the electrode of the semiconductor chip 20 with the terminal 12 formed on the surface of the circuit board 10. This causes the desirable electrical connection of the conductive bump 22 formed on the electrode of the semiconductor chip 20 with the terminal 12 formed on the surface of the circuit board 10 to be damaged.
Also, when semiconductor chip 20 is surface-mounted onto the circuit board 10 via the ACF resin by the above-mentioned process, gas generated from the resin of the ACF 30 during the heating or air dwelling in the inside of the ACF 30 and expanding during the heating is expelled to the outer air encircling the semiconductor chip 20 through the ACF 30 interposed between the semiconductor chip 20 and the circuit board 10, which is softened during the heating.
However, when the semiconductor chip 20 is surface-mounted to the circuit board 10 by the above-mentioned process, all the gas or air in the interior of the ACF 30 is not suitably expelled to the outer air encircling the semiconductor chip 20 through the softened ACF 30, but tends to dwell in the inside of a portion of the ACF 30 in the peripheral region of the semiconductor chip 20 which is free from the pressure from the semiconductor chip 20, forming voids 32 therein, as shown in FIG. 6.
Therefore, the reliable bonding is not obtainable between the semiconductor chip 20 and the surface of the circuit board 10 via the resin of the portion of the ACF 30 wherein the void 32 is formed.
As a result, if the semiconductor chip 20 is surface-mounted onto the circuit board 10 by the above-mentioned process, the semiconductor chip 20 bonded to the circuit board 10 via the resin of the ACF 30 has been liable to be stripped off from the surface of the circuit board 10 during use, whereby the electrical connection between the conductive bump 22 formed on the electrode of the semiconductor chip 20 and the terminal 12 formed on the surface of the circuit board 10 is damaged.
The same is true of a semiconductor chip 20 surface-mounted onto a circuit board 10 by bonding the semiconductor chip 20 with the surface of the circuit board 10 via an electro-insulating film of thermosetting or thermoplastic resin, in the same manner as described above, wherein conductive bumps 22 formed on the semiconductor chip 20 are electrically connected to terminals 12 formed on the surface of the circuit board 10.